U.S. patent number 5,299,666 [Application Number 07/950,794] was granted by the patent office on 1994-04-05 for resettable pilot operated torque limiter.
This patent grant is currently assigned to Sundstrand Corporation. Invention is credited to Gary Gillingham, David J. Lang, Eric Stoutenborough.
United States Patent |
5,299,666 |
Lang , et al. |
April 5, 1994 |
Resettable pilot operated torque limiter
Abstract
Volume, weight and complexity difficulties in the fabrication of
torque limiters are avoided in a construction including a housing
(10), a shaft (20) journalled in the housing (10) and adapted to be
connected to a source (22) of rotary power, and a rotary output
(28) journalled in the housing (10). A ball ramp coupling (44) is
disposed within the housing (10) and includes an axially movable
drive element (46) coupled to the shaft (20), a driven element (42)
coupled to the output (28), a spring (52) biasing the elements
(42,46) towards each other, facing ramps (61,62) in the elements
(42,46) at the interface of the elements and balls (64) in the
ramps. A first set of teeth (72) is carried by the drive element
(46) while a second set of teeth (82) is carried by the housing
(10) and aligned with the first set of teeth (72). When resistance
to rotation of the output ( 28) is encountered relative movement
between the elements (42,46) will occur which in turn will cause
the ball (64) to move the drive element (46) axially relative to
the driven element (42) causing the teeth (72,82) to engage to halt
further torque transmission between the input shaft (20) and the
output (28).
Inventors: |
Lang; David J. (Rockford,
IL), Stoutenborough; Eric (Rockford, IL), Gillingham;
Gary (Cherry Valley, IL) |
Assignee: |
Sundstrand Corporation
(Rockford, IL)
|
Family
ID: |
25490861 |
Appl.
No.: |
07/950,794 |
Filed: |
September 24, 1992 |
Current U.S.
Class: |
188/134;
192/223.2 |
Current CPC
Class: |
F16D
7/08 (20130101); B64C 13/34 (20130101); F16D
67/02 (20130101); F16H 35/10 (20130101) |
Current International
Class: |
F16D
67/00 (20060101); F16D 67/02 (20060101); B64C
13/00 (20060101); B64C 13/28 (20060101); F16D
7/08 (20060101); F16D 7/00 (20060101); F16H
35/10 (20060101); F16H 35/00 (20060101); F16H
057/10 () |
Field of
Search: |
;188/134,82.9
;74/411.5,412TA ;192/8R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kashnikow; Andres
Assistant Examiner: Muratori; Alfred
Attorney, Agent or Firm: Wood Phillips VanSanten Hoffman
& Ertel
Claims
We claim:
1. A torque limiter comprising:
a housing;
a shaft journalled in said housing and adapted to be connected to a
source of rotary power;
a rotary output journalled in said housing;
a ball ramp coupling within said housing including an axially
movable drive element coupled to said shaft, a driven element
coupled to said output and facing said drive element, a spring
biasing said elements toward each other, facing ramps in said
elements at the interface of said elements and balls in said
ramps;
a first set of teeth carried by said drive element;
a second set of teeth carried by said housing and aligned with said
first set;
whereby, when a predetermined resistance to rotation of said output
is encountered, relative movement between said elements will occur,
which in turn will cause said balls to move said drive element
axially relative to said driven element, said relative axial
movement causing the teeth of said first set to engage with the
teeth of said second set; and means mounting said second set of
teeth for limited axial/rotational movement within said
housing.
2. The torque limiter of claim 1 further including second and third
spring means acting oppositely on said second set of teeth to
normally locate said second set of teeth at an intermediate
location between the extremes of its limited axial movement.
3. The torque limiter of claim 2 wherein said mounting means
comprise a plurality of circumferentially spaced pins and said
second spring means comprise compression coil springs impaled on
respective ones of said pins.
4. The torque limiter of claim 3 wherein said third spring is a
wavy spring interposed between said housing and said second set of
teeth and about said shaft.
Description
FIELD OF THE INVENTION
This invention relates to torque limiters as, for example, torque
limiters that may be interposed between a power drive unit and an
aircraft control surface to be driven thereby.
BACKGROUND OF THE INVENTION
It is often necessary to use torque limiting devices in association
with other machinery or equipment to prohibit the transfer of
torques above some predetermined value so that damage to associated
machinery or equipment does not occur. One typical application is
an aircraft. Prime movers known as power drive units (PDU's),
typically hydraulically powered, are utilized to move control
surfaces of the aircraft as, for example, slats or flaps, between
various positions. If movement of such an element is resisted as
for example, by a mechanical jam in the drive line or some exterior
influence exerting a force against the control surface preventing
its movement, the power drive unit will tend to stall. Such units
have high stall torques and as a consequence, if no steps are taken
to prevent it, the stall torques can cause damage to the control
surfaces, to the drive line, to the aircraft frame or all of the
above.
A typical torque limiting device is illustrated in U.S. letters
patent 4,030,578 issued Jun. 21, 1977 to Cacciola et al. In devices
of this sort, a brake disc pack is employed and is compressed
against a non-rotatable object as, for example, part of a housing.
The compression is against the bias of a spring and the excess
torque is taken up in the brake disc pack and grounded to the
housing. Clearly, the coefficient of friction is a controlling
factor in the amount of torque being taken up or absorbed within
the brake disc pack.
Furthermore, the compression of the brake disc pack is obtained as
a result of a ball ramp coupling that is interposed between the
input to the torque limiter and the output thereof. In
constructions such as that shown in the above-identified Cacciola
et al patent, it is necessary that the balls in the ball ramp
coupling be constructed of sufficient size so as to be capable of
transmitting all of the torque up to the stalled torque level of
the PDU to the brake disc pack to be absorbed thereby.
As a consequence of this type of construction, torque limiters have
been fairly large and relatively unwieldy. They are unnecessarily
heavy and thus impose a weight penalty in the environment in which
they are most often used, namely, aircraft.
The present invention is directed to overcoming one or more of the
above problems.
SUMMARY OF THE INVENTION
It is the principal object of the invention to provide a new and
improved torque limiter. More specifically, it is an object of the
invention to provide a torque limiter having a relatively few
parts, and which may be constructed of relatively small size to
thereby be compact and light weight.
An exemplary embodiment of the invention achieves the foregoing
object in a construction including a housing including a rotary
input and a rotary output. An expandable coupling is contained
within the housing and has a drive element coupled to the input, a
driven element coupled to the output, and one of the elements
mounted for axial movement with respect to the element to which it
is coupled. Means are included which extend between the elements
and are operable to normally transmit torque from the drive element
to the driven element up to a predetermined value and thereafter
cause the axial movement of the one element. Two sets of teeth are
provided. One is carried by the one element and the other is
carried by the housing and both sets are disposed to engage with
one another upon axial movement of the one element. As a
consequence, the number of parts and the size of the torque limiter
are reduced by elimination of a brake pack.
In a highly preferred embodiment, the one element is the drive
element. In this embodiment of the invention, the expandable
coupling need be sized only sufficiently large so as to transmit
torque up to the predetermined value. The excess torque applied to
the input is grounded to the housing on the input side rather than
on the output side of the mechanism, thereby allowing a downsizing
of the expandable coupling.
In a highly preferred embodiment, the coupling is a ball ramp
coupling.
One embodiment of the invention contemplates a torque limiter that
includes a housing together with a shaft journalled in the housing,
which shaft is adapted to be connected to a source of rotary power.
A rotary output is journalled in the housing and a ball ramp
coupling is located within the housing. The ball ramp coupling
includes an axially movable, drive element coupled to the shaft, a
driven element coupled to the output and facing the drive element,
a spring biasing the elements towards each other, facing ramps in
the elements at the interface of the elements and balls in the
ramps. A first set of teeth are carried by the drive element and a
second set of teeth are carried by the housing in alignment with
the first set. Consequently, when a predetermined resistance to
rotation of the output is encountered, relative movement between
the elements of the ball ramp coupling will occur which, in turn,
will cause the balls to move the drive element axially relative to
the driven element. The relative axial movement will cause the
teeth of the first set to engage the teeth of the second set to
ground out the input so that excess torque is delivered to the
housing rather than to the output. In a highly preferred
embodiment, the teeth of the sets have negative rake angles.
A preferred embodiment contemplates that the drive element be
splined to the shaft for axial movement thereon. The drive element
also is provided with opposed faces. One ramp of each ramp pair is
in one of the faces and the teeth of the first set extend axially
from the other of the faces of the drive element.
The invention also contemplates the provision of means mounting the
second set of teeth for limited axial movement within the
housing.
Preferably, second and third spring means are acting oppositely on
the second set of teeth to normally locate the second set of teeth
at an intermediate location between the extremes of its limited
axial movement relative to the shaft.
In a highly preferred embodiment, the mounting means comprise a
plurality of circumferentially spaced pins and the second spring
means comprise compression coil springs impaled on respective ones
of the pins.
In a highly preferred embodiment, the third spring is a wavy spring
interposed between the housing and the second set of teeth and
disposed about the shaft.
Preferably, the output comprises a sleeve on the shaft and has a
gear on its exterior surface.
Other objects and advantages will become apparent from the
following specification taken in connection with the accompanying
drawings.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view of an actuator including a torque
limiter made according to the invention;
FIG. 2 is a fragmentary, somewhat schematic illustration of ball
ramps in a ball ramp actuator employed in the invention; and
FIG. 3 is a fragmentary developed view taken approximately along
the line 3--3 in FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
An exemplary embodiment of the invention includes a housing,
generally designated 10, made up of housing halves 12 and 14. Each
of the housing halves 12 and 14 mounts bearings 16,18 which serve
to journal a rotary shaft 20. The shaft 20 is an input shaft and
typically will be connected to one or more power drive units or
PDU's, one of which is shown schematically at 22. In the usual
case, several of the actuators may be spaced out along the length
of a wing or the like and be splined to one another so that a
single PDU 22 may drive several of the actuators.
In reality, one end of the shaft 20 is journalled by a bearing
surface 24 on the interior 26 of a sleeve 28. The sleeve 28 is in
turn journalled by the bearing 18 as well as by an axially spaced
bearing 30 within the housing half 12. On its exterior surface 32,
the sleeve 28 includes a gear formation defined by teeth 34. The
sleeve 28 thus serves as a rotary output from the housing which may
be coupled to, for example, a gear 35 which in turn may be coupled
via any rotary to reciprocating a motion converting mechanism to a
flap or a slat.
A spline 36 couples the sleeve 28 to a ring 38 within the housing.
On its radially outer surface, the ring 38 includes an additional
spline 40 which is coupled to a driven element 42 forming part of a
ball ramp coupling, generally designated 44. The drive element of
the ball ramp coupling 44 is designated 46.
Thrust bearings 50 are employed where indicated and a compression
coil spring 52 is impaled by the shaft at a location on the side of
the drive element 46 opposite from the driven element 42. The
compression coil spring 52 biases the drive element 46 toward the
driven element 42 at some predetermined preload. The compression
coil spring 52 is held at the desired preload by means of a washer
54 surrounding the shaft 20 which in turn is held in place by a
lock ring 56.
As is well known, facing sides 58 and 60 of the driven element 42
and drive element 46 respectively are provided with pairs of ball
ramps. As seen in FIG. 2, one ball ramp 61 is formed in the driven
element 42 and another ball ramp 62 is formed in the face 60 of the
drive element 46. The ball ramps 61 and 62 will be in nominal
alignment with one another and a spherical ball 64 located to be
partly disposed in each ball ramp 61 and 62 constituting a pair.
Typically, three of the pairs will be located in the faces 58 and
60 at 120 degree increments thereabout.
As is well known, if relative rotary motion occurs between the
elements 42 and 46, the balls 64 will tend to ride up their
respective ramps and in so doing, exert a separating force between
the faces 58, 60 of the elements 42, 46. This in turn will drive
the drive element 46 to the left as viewed in FIG. 1. By
appropriately selecting the spring 52 and the preload thereof, the
maximum torque transmitted from the drive element to the driven
element 42 via the balls 64 may be appropriately chosen, such that
when the predetermined torque level is exceeded, as, for example,
there is a jam in the system resisting rotary motion of the output
sleeve 28, the spring 52 will exert insufficient force to keep the
elements 42 and 46 in the relative positions illustrated in FIG.
1.
To absorb excess torque, it is desirable to ground the shaft 20.
That is to say, it is desirable to halt rotation of the shaft 20 to
prevent damage to equipment that may be driven thereby.
To this end, the drive element 46 has a face 70 opposite the face
60. Extending axially from the face 70 are a series of teeth 72. As
can be seen in FIG. 3, each side of each tooth 72 includes a
diagonally inwardly extending surface 74 or 76 which defines a
negative rake angle for both sides of the associated tooth 72.
A disc 80 mounted within the housing also carries axially extending
teeth 82 which are aligned with and directed toward the teeth 72.
Like the teeth 72, the teeth 82 have negative rake angles on both
sides thereof as can be seen in FIG. 3.
A series of axially directed pins 84 (only one of which is shown)
have their ends in respective bores 86 and 88 in the housing halves
12 and 14 respectively. The pins 84 extend through notches 90 in
the periphery of the disc 80. The notches thus serve with the pins
to mount the disc 80 for limited axial/rotational movement within
the housing 10.
Compression coil springs 92 are provided and one is disposed about
each of the pins 84 to be compressed against the housing half 12
and the right-hand side of the disc 80. Thus, the compression coil
springs 92 (only one of which is shown) serve to bias the disc 80
to the left as viewed in FIG. 1.
A ring-like wavy spring 94 is disposed about the shaft 20 outwardly
of the compression coil spring 52 to be interposed between the
housing half 14 and the left-hand side of the disc 80 to exert an
opposing bias against the disc 80. That is to say, the wavy spring
94 biases the disc 80 to the right as viewed in FIG. 1.
The arrangement is such that under normal conditions, the disc 80
occupies a position somewhere between the extreme limits of its
travel within the housing 10. In this regard, a space 98 exists
between the disc 80 and the housing half 14 under normal
circumstances while a space 100 exists between the teeth 72 and 82
on the opposite side of the disc 80. When torque loading increases,
relative rotation between the driven element 42 and the drive
element 46 will occur as mentioned previously. The balls 64 will
cause separation of the elements 42 and 46 with the later being
moved axially to the left as viewed in FIG. 1. This will result in
the teeth 72 coming into engagement with the teeth 82 and by reason
of the negative rake angles on each, they will be drawn into firm
abutment solidly locked together. Because the disc 80 which carries
the teeth 82 is prevented from rotating by reason of its mounting
on the pins 84, the stall torque of the PDU 22 will be transmitted
to the housing 10 upon such lockup occurring. Of course, since the
shaft 20 is prevented from rotating at his time, there can be no
driving of the output sleeve 28 and damage to downstream components
cannot occur as the excess torque is not being transmitted to
them.
To set the device, it is only necessary to reverse the direction of
rotation of the shaft 20. This will cause the teeth 72 to disengage
from the teeth 82. The compression coil springs 92 upon
disengagement of the teeth 72,82 will urge the disc 80 to the left
as viewed in FIG. 1. At the same time the compression coil spring
52 will be urging the drive element 46 to the right. Because
relative movement will occur between the elements 42 and 46 at this
time, allowing the balls 64 to seat within the depths of the
respective ball ramps 61,62 which in turn will allow the drive
element 64 to move back to the position shown in FIG. 1 with the
teeth 72 fully disengaged from the teeth 82.
If, during the engaging procedure, the axial faces of the teeth 72
and 82 abut one another preventing engagement, the ring 80 may move
to the left as viewed in FIG. 1 across the space 98 against the
bias of the wavy spring 94. This allows the teeth 72 to slip off of
the teeth 82 and drop into the space between adjacent teeth so that
upon a small amount of additional rotary movement, lockup will
occur.
From the foregoing, it will be appreciate that because balls 64
need never transmit excess torque for the mechanism to be
operative, they may be made only of that size required to transmit
the predetermined amount of torque to the mechanism being driven.
This permits smaller balls 64 to be utilized and permits the
overall structure to be smaller.
Moreover, elimination of the brake disc pack in favor of the teeth
eliminates a number of components to provide a simple construction
and additionally allows a further decrease in the overall volume of
the mechanism.
The use of the teeth provides for positive locking so that
operation at the right point is not dependent on the coefficient of
friction. Furthermore, location of the grounding mechanism, i.e.
the disc 80 and teeth 82 on the input side of the mechanism and
other constructional features described herein, allows the use of
relatively high angles for the ramps 61 and 62 which, in turn,
reduce the size of the springs required to achieve desired
operation. In effect, the balls 64 are used as a sensor for a
overload situation thus act as a pilot causing engagement of the
brake which in turn is defined by the inter-engaging teeth
72,82.
All in all, a highly reliable, simple to construct, relatively
small volume and low weight torque limiter is provided.
* * * * *